Field of the Invention
The embodiments of the present invention relate to an electric machine and display method.
Related Art
An electric machine such as an injection molding machine or a machine tool is driven by a motor. The torque of the motor of the electric machine is normally restricted by an upper limit of a current. To restrict a current flowing in the motor to a value equal to or lower than the upper limit, a threshold (a limit value) is set in a current instruction or a current detection value. When the current instruction or the current detection value exceeds the limit value, the electric machine clamps the current instruction to the limit value.
The upper limit of the current is kept at a high value when the rotational speed of the motor is relatively low. Therefore, the torque of the motor can be increased to be relatively high. However, when the rotational speed of the motor becomes relatively high, an induced voltage from the motor becomes close to a voltage applied to the motor and a voltage saturation state occurs, which decreases the upper limit of the current. Accordingly, when the rotational speed of the motor is relatively high, the torque of the motor cannot be increased to be so high. Therefore, it is preferable that the motor has a preferable range of a relation (hereinafter, “T-N characteristics”) between the torque and the rotational speed of the motor and is controlled not to exceed the range of the T-N characteristics.
Conventionally, there is a case that when the torque or the rotational speed of the motor exceeds the preferable range of the T-N characteristics, the electric machine provides a warning indicating that the current has exceeded the upper limit to a user. For example, in the case of an injection operation of an injection molding machine, when the current exceeds the upper limit or the voltage saturation state occurs during the injection operation, there is a possibility that the motor cannot be controlled appropriately. In this case, the motor may vibrate abnormally or may break the machine or a mold. Accordingly, the electric machine provides a warning indicating that the current has exceeded the upper limit to a user.
The user can relax the operation condition of the motor in response to the warning. However, the user cannot know a margin produced by the relaxing of the operation condition to the upper limit of the current. It is also difficult for the user to know a load status on the motor in a motor operation condition.
The present invention has been achieved to solve the above problems and an object of the present invention is to provide an electric machine and a display method that enable a user to easily know a load applied on a motor.